The model system of classical conditioning of the eyeblink response in rabbits an(i humans has he potential to elucidate brain mechanisms involved in learning, memory, and aging. Considerable evidence exists that memory has at least two major forms: one requiring conscious recollection of specific learning episodes ("explicit" memory), and the other involving the expression of learning hat is automatic, without conscious or deliberate recollection ("implicit" memory). Studies of classical conditioning in human aging are of particular significance because data may elaborate or challenge theoretical perspectives on memory systems. Research is proposed: (a) to describe more extensively age differences in classical conditioning over the adult human life span, (b) to test hypotheses about mechanisms involved in age effects on classical conditioning, and (c) to explore he cohesion of the theoretical construct of implicit memory in normal older adults and patients with focal brain lesions. A major aim of the first study is to determine the age period when the largest age differences in eyeblink conditioning occur. Adults aged 30-99 years will be classically , conditioned and will be assessed on a battery of neuropsychological tests. We hypothesize that age differences will emerge in the period between 45 and 55 years of age -- a period when the decline in reaction time and Purkinje cell loss accelerate. Simple reaction time and neuropsychological measures of timing (cerebellar function) should be the best predictors of efficiency of classical conditioning. A major aim of the second study is to determine whether there are conditions of optimal timing of the CS-US interval between the conditioned and unconditioned stimulus for middle-aged and older adults when associative learning will be equal to that in the young. A major tim of the third study is to determine how much of the effect of age on classical conditioning is due to health. A major aim of the fourth study is to explore brain memory systems in patients with focal lesions and the role of focal brain damage in implicit and explicit memory tasks. Data from :his project will link behavioral aging effects to the cerebellum and associate learning and memory deficits in aging to this brain structure which is understudied by gerontologists. Results will extend he empirical base of knowledge on aging and eyeblink classical conditioning as a form of implicit memory. We expect to demonstrate that implicit memory tasks are performed in a consistent manner in focal lesion patients, but are dissociated (with some implicit memory tasks showing stability while others show decline) in normal aging when brain changes are not focal.